The present invention relates to a method of forming in place a female fastener bore opening and the fastener which, in the disclosed embodiment, is a a hat-shaped nut fastener sealed at the opposed bore openings.
Hitherto hat-like fastener elements are known, e.g. in the form of cap or dome nuts, with an inner passage or bore which is provided with a fastening means, such as a thread or a bajonet socket and is closed at one end by means of a transverse wall. It is also entirely possible, and indeed preferred, for the fastener element to also have a rivet section at one end which can be inserted into a premanufactured aperture in a metal part and deformed by a riveting process in order to obtain a form-fitted connection between the fastener element and the sheet metal part.
Such hat-like fastener elements are known per se and are also of advantage when one is concerned with closing-off the thread of the fastener element or a bayonet connection at one end so that contamination can not penetrate into the thread.
As the fastening means, normally in the form of a thread, is normally located on the one side of the sheet metal part, while the mating screw is screwed into the nut element from the other side of the sheet metal, the riveted connection does not have to bear special forces in the assembled state of the fastener element, but rather, as a result of the threaded connection, an annular ring shoulder of the nut element on the same side of the sheet metal as the thread of the nut element is pressed by the clamping force of the screw against the sheet metal, with the riveted connection itself being largely relieved. Such cap nuts are thus also suitable for use in highly loaded screw connections.
A problem is however encountered when the sheet metal part with the attached hat-like fastener element has to be treated by further process steps before final assembly. Such further treatments include, for example, sand blasting, painting- in particular immersion painting and also the application of other protective layers. Through all these further treatment steps, the danger exists that the thread or the fastener means in the interior of the hat-like fastener element can be blocked or damaged so that it must either be freed from blockages or deposits in time consuming manual labor, or must indeed be scrapped.
It is known in the art to protect hollow cavities in critical components by plastic plugs which can be inserted and removed again. An example for this is a metal brake cylinder, the fluid supply opening of which is provided with a thread and is frequently also closed by a hat-shaped plastic plug. A problem with this solution is, however, not only that the closure plugs can be lost, but rather also that, with mass production, a large number of plastic plugs are required which must then be disposed of.
The present invention is based on the object of providing a fastener element or a sheet metal part with an attached fastener element which is so designed that an effective protection is achieved against blockage of or damage to the fastening means and also against deposits in the fastening means, without the parts which ensure protection being easily lost and leading to disposal problems, and with the fastener element being inexpensive to manufacture, for which purpose a special manufacturing process and a tool for the manufacturing of the fastener element should likewise be provided in accordance with the invention.
The method of sealing a fastener bore opening of this invention includes supporting a heat softenable plastically deformable sealing element in the bore opening having a diameter which is less than the bore opening, heating the sealing element to its softened plastically deformable temperature, then deforming the sealing element radially outwardly into mechanical interlocking engagement with the bore opening, which seals the bore opening when the sealing element cools. In the preferred method, the sealing element is deformed radially as described by a ram which is reciprocated through the bore opening into engagement with the sealing element. In the most preferred method of this invention, the sealing element is supported on a die member in the bore opening and the ram, which in the most preferred embodiment is heated, deforms the sealing element in the die member into mechanically interlocking relation with the female fastening element in the bore opening. As described, the female fastening element may be a threaded portion in the bore or a bayonet connection. Where the ram is heated, the ram simutaneously heats and radially deforms the sealing element in the fastener bore, as described.
The sealing element or closure plug is so deformed that it enters into a form-fitted connection with the fastener element and thus can not be easily lost, and together with the transverse wall protects the interior of the fastener element with the fastening means, i.e. with the thread or the bayonet socket, against the penetration of undesired media such as paint, rubber, plastic or underseal. Since the plastic closure plug which has been deformed to a type of disc can be pressed inwardly, the path to the thread or to the bayonet socket is first exposed by displacement of the closure plug on insertion of the screw. The closure plug is then preferably received in a receiving chamber formed at the end of the fastener means adjacent the transverse wall and thus remains within its completed fastening. In this manner, the disposal of the closure plugs in the factory where the sheet metal part is manufactured is not necessary at all. On scrapping the article, for example a motor car, the few closure plugs which are built into the car are disposed of through the melting down of the metal.
The closure plugs could indeed consist of a soft metal for example a lead alloy or aluminum, however preferred are closure plugs of thermo-plastic polymeric material, such as polyethylene, since these are usually deformable with a low expenditure of force on simultaneous heating, but readopt a solid form again after deformation and are thus protected against loss.
In a fastener element with the form of a nut with an inner thread, the closure plug is preferably retained by a form-locked fit with the thread at the entry to the thread. In this way the thread serves a double purpose in that it functions on the one hand as a fastening means, and on the other hand, however, also forms the desired form-fitted seat for the deformed closure plug. It is accordingly not necessary to provide a special seat for the deformed closure plug, for example in the form of a special undercut, so that the constructional length of the fastener element is not unnecessarily increased and the manufacturing costs are reduced.
In this design the closure plug preferably projects, in at least substantially sealed manner into at least one thread turn, preferably to approximately two and a half thread turns, but should not however completely fill these out, but rather should have a spacing from the root of the thread turns and be at least substantially rounded, and preferably approximately semicircularly rounded, at its side facing the root of the thread turns. This design of the closure plug in the deformed state ensures on the one hand the sealing of the thread, and also ensures that the closure plug cannot be easily lost. On the other hand this design also facilitates the pressing of the closure plug into the thread or into a receiving chamber at the far end of the thread.
It is particularly favorable when the closure plug has a cup-shaped recess at the side facing the interior of the hat-like element, preferably a recess with a slightly concavely rounded base. Furthermore, the closure plug should have a slightly convexly curved surface at the outer side which extends at least substantially parallel to the slightly concavely extending base of the cup-shaped or pot-like recess. Through this design the pressure forces which are exerted during a sand blasting treatment or during an immersion treatment on the closure plug, only lead to a slight flattening of the closure plug, whereby the latter is pressed more firmly into its seat at the start of the thread. On the insertion of a screw a somewhat higher force can however be applied so that the initially convexly outwardly directed base of the closure plug is deformed into a convexly inwardly arched form, whereby the closure plug is lifted out of the thread and can then be pressed with little force to the far end of the thread.
It would also be conceivable to form the closure plug so that it is penetrated by the screw and thereafter forms a plastic ring which serves to secure the inserted screw against rotation.
As already indicated, a receiving chamber for the closure plug which has been displaced from its seat is preferably provided, with this receiving chamber lying in the interior of the hat-like fastener element close to the transverse wall and being formed as a ring chamber. The receiving chamber preferably has a diameter which corresponds, at least substantially, to the outer diameter of the counter element or to the outer diameter of the thread, but which is not smaller than the latter.
The transverse wall itself is preferably formed by a disc, in particular a disc generated during a stamping process. This disc preferably sits on an annular or ring-shaped shoulder of the fastener element and closes the receiving chamber for the plug at the end face of the element remote from the thread. The disc itself is preferably retained by a radially inwardly directed, annular rivet rim formed from the material of the fastening element, with the rivet rim and the ring shoulder forming a radially inwardly open ring groove in which the periphery of the disc is held in form-fitted manner.
The invention also includes a sheet metal part with at least one hat-like fastener element of the previously described kind which is secured therein by a riveting process. The sheet metal part can also be a semi-finished product which is sand blasted or particle blasted on at least one face and is covered with a plastic, rubber or paint layer. Three specific examples for such sheet metal parts are, for example, a suspension strut mount of a vehicle, an engine bearer consisting of sheet metal and rubber for a vehicle, or a mounting device for an anti-roll bar consisting of a sheet metal bracket with inserted rubber.
A particular method for the manufacture of a hat-like fastener element, in particular a fastener element as previously described, wherein the hat-like mounting element has an inner passage which is provided with a fastening means, such as a thread or a bayonet socket, and is closed at or close to one end by means of a transverse wall, with the fastener element preferably having a riveting section at one end, is characterized in that a closure plug consisting of a deformable material is introduced into the fastener element which is at least partly received in a matrix and is squashed and plastically deformed between the matrix and a ram moved into the passage in such a way that it is held in a form-fitted manner in a seat provided within the fastener element and hereby closes the one end of the passage; and in that the respective other end of the passage is subsequently closed by a disc forming the transverse wall which is placed on a ring shoulder of the fastener element and is preferably retained in contact with this ring shoulder by a rivet rim formed by a forming process from the material of the fastener element.
Whereas, with a customary sealing technique requiring the insertion of a removable plug, this plug is inserted into the otherwise finished fastener element, in the method of the invention the closure plug is first inserted and then the disc forming the transverse wall. This method makes it possible to apply to the closure plug the forces which are necessary to deform it. When the closure plug consists of thermo-plastic polymeric material, then the ram is preferably heated, to reduce the force required for deformation of the plug. Here the temperature of the ram should be selected so that the plug does not melt, but rather simply becomes softened or somewhat pasty and can easily be brought into the final form. Through the deformation of the closure plug, the latter then also comes into contact with an extended surface of the hat nut element and also the matrix, whereby heat is withdrawn from the closure plug, and at least an initial solidification is achieved which ensures that the ram can be removed without simultaneous removal of the closure plug. A spray mist of a parting agent can be sprayed into the passage of the nut, or onto the end face of the ram, so that the ram does not stick to the closure plug. In similar manner a small quantity of a parting agent can previously be sprayed into the toolholder in order to avoid a sticking of the closure plug here.
The disc is preferably formed by a slug stamped out of a piece of sheet metal which represents a favorably priced possibility for the manufacture of the disc, and thus of the fastener element.
The toolholder preferably contains a movable ejection pin which serves for the ejection of the fastening element after the insertion of the closure plug and presses against a metallic surface of the fastener element. In this way it is prevented that the ejection pin solely presses on the plastic plug and possibly prematurely displaces the plug from its seat.
When the method is carried out with a movable ejection pin then the end face of the ejection pin is preferably also exploited for the squashing process in the sense that it serves as the counter pressure element to the ram.
The method is preferably carried out as follows with a multi-station tool:
a) in a first station the fastener elements are individually received in the matrices,
b) in a second station, which can optionally be integrated into the first or third station, and then omitted as a separate station, the balls forming the closure plugs are individually inserted into the respective fastener elements,
c) in a third station the ram is moved into the passage of the fastener element to squash and deform the ball forming the closure plug and, on laying out of the tool for closure plugs consisting of thermo-plastic material, the ram is heated,
d) in a fourth station a piece of sheet metal in strip form is guided transverse to the direction of movement of the fastener elements through the stations over the still open end face of the respective fastener element and, while using the open end face of the respective fastener element as a stamping matrix, a disc-like stamping slug is stamped out of the sheet metal and placed in firm contact against a ring shoulder of the respective fastener element by means of a stamping tool,
e) in a fifth station the edge of the respective fastener element which projects upwardly above the stamped slug is formed by means of a forming tool into a radially inwardly directed rivet rim, and hereby the stamped slug is fixed in form-fitted manner in the respective fastener element, and
f) in a sixth station the finished hat-like fastener elements are ejected by means of an ejection pin movably arranged in the matrix, wherein a plurality of matrices are provided and are movable around a transport circuit from station to station in order to hereby bring about the transport of the respective fastener elements into the various stations.
The invention will now be explained in more detail with reference to embodiments and to the drawing in which are shown: